The objective is the preparation, under mild "biological type" condtions, of compounds containing cyclopropane rings with special emphasis on those of biological importance, such as lactobacillic acid and bresqualene pyrophosphate. The proposed method involves the treatment of an olefin and a transition-metal compound with an ylide derived by treating a sulfonium salt with an amine. Attempts will be made to facilitate the formation of the assumed carbene-metal intermediate by buiilding into the ylide functional groups which along with the ylide carbon atom are capable of chelating the metal.